Bret Michaels remains in critical condition at an undisclosed hospital, and doctors still haven't found the source of bleeding onto his brain that is affecting his speech and vision, according to the singer's website.

The 47-year-old reality TV star and frontman of the glam-metal band Poison has been hospitalized since late Thursday after suffering a massive subarachnoid hemorrhage, or bleeding at the base of his brain stem, his publicist confirmed to ABCNews.com Friday.

"At this point Bret remains in ICU in critical condition," read a statement posted on bretmichaels.com Sunday. "He is under 24 hour doctors care and supervision. We are hopeful that further tests will locate the source of the bleeding, which has still not been located. As we all know Bret is a fighter and we are hopeful that once all is complete the slurred speech, blurred vision and dizziness, etc. will be eliminated and all functions will return to normal."

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Bret Michaels Suffers Brain Hemorrhage

There were reports Saturday that Michaels had been downgraded from critical condition, but bretmichaels.com called those "incorrect reports."

Still, Michaels' father, Wally Sychak, sounded encouraged when he spoke to the website RadarOnline.com on Friday about a phone conversation with Michaels.

"I talked to him this morning. He sounded upbeat and positive but they had him sedated," Sychak said. "But he's doing good. He sounded like my son."

The latest medical woes for Michaels, a diabetic, came just days after an emergency appendectomy he received after falling ill before a concert April 11.

Besides his active performing career, Michaels can be seen each week as a top contender on Donald Trump's NBC reality show "The Celebrity Apprentice," competing against singer Cyndi Lauper and media maven Sharon Osbourne, to name a few of the remaining competitors. He previously starred in VH1's "Rock of Love With Bret Michaels."

Trump released a statement Friday, saying, "I am deeply saddened to hear about Bret Michaels and my thoughts and prayers are with him and his family at this time. He's a great competitor and champion and I hope he will be fine."

The bretmichaels.com statement Sunday offered thanks for such well wishes.

"Everyone at Michaels Entertainment would like to thank all fans and friends for their continued thoughts and prayers through this difficult time," the statement read.

Details of Appendectomy and Recovery

Last weekend, Michaels revealed details of how he was rushed to a hospital on April 11 before a show in San Antonio, Texas. At the time, he said he still was not recovered.

"They told me that if I had gone onstage like I wanted to, [my appendix] likely would have ruptured and I could have died," he wrote on his blog.

"I'm feeling pretty bad ... to tell you the truth," Michaels wrote after the appendectomy. "When you're not planning on having a body part ripped out of you, it can be a shock to the system. While the doctors are amazing in San Antonio, there is just no way around the fact that getting your appendix out HURTS. I have a pretty good threshold for pain, but this one hurts."

The rocker added that because he's been a diabetic since age 6, his recovery could take longer than usual. However, it's unlikely that Michaels' diabetes spurred his current condition.

"This [type of hemorrhage] is usually from an aneurysm," Dr. Wendy Wright, an assistant professor of neurology and neurosurgery at Emory University Hospital in Atlanta, told ABCNews.com. "The risk of an aneurysm rupturing is probably related to size -- the larger the aneurysm, the more likely to rupture -- and also may be more likely in people who smoke or on blood thinning medications."

Past Drug Use Could be a Factor in Impairing Recovery

A factor that could have played into Michaels' current condition is his past history of drug use. Michaels hasn't been shy about his hard-partying, rock 'n' roll past. In a 2003 interview with VH1, he described a "menage a mess" from his Poison days, saying, "It was the drugs, the booze, doing the lines off [exotic dancers]."

"Being a drug user, in particular a user of injectable drugs, can damage heart valves and predispose you to get endocarditis," said Dr. Richard Bernstein, a neurologist at Northwestern Memorial Hospital.

Endocarditis involves infection at one of the heart's valves.

Bernstein added: "Cocaine use in and of itself can be a major cause of intracerebral hemorrhage."